1. Field of the Invention
This invention relates to the calibration of instruments used to detect or monitor gas and, more particularly, to methods and devices for easily, quickly and inexpensively testing the calibration of a gas detector.
2. Description of the Prior Art
Gas detectors are known to become inaccurate through use or the passage of time, or both. It is a common practice to adjust the instrument so as to maintain accurate sensitivity. Typically, a test gas of known composition is passed through the gas detector to determine whether the reading developed by the instrument accurately reflects the composition of the test gas. Full calibration procedures must be undertaken periodically to assure accuracy of the instrument. However, it is frequently desirable to make a cursory check of the instrument's operation without going through the full effort and expense involved in formal calibration procedures.
Presently, there exists no known, low cost and effective method for performing both intermediate and full calibration procedures on sophisticated gas detectors. A typical calibration kit for such instruments, including a regulator, valving, a large air cylinder and a flowmeter, can cost up to $350.00. The user incurs a tremendous expense just to determine if the instrument is working properly. See, for example, U.S. Pat. No. 4,723,436. Other arrangements are shown in U.S. Pat. Nos. 4,287,750, 4,322,964 and 4,460,448.
Previous attempts have been made to devise simple, manageable systems for calibrating gas detectors. One such apparatus is disclosed in U.S. Pat. No. 4,722,217 to Arnett et al., which focuses on calibration of gas detectors used in systems delivering anesthesia to hospital patients. The Arnett et al. patent discloses a calibration test gas container connected by tubing to the inlet of a gas detector. The valve on the container is manipulated, along with the detector's pumping means, to stall a test gas within the detector, exposing the gas to the detector's sensor. Distensible container means are also disclosed for use in avoiding over-pressurization of the gas detector system.
U.S. Pat. No. 4,462,244 to Lee discloses an apparatus for field testing smoke detectors. A drum-like container is provided with an air impeller and carries therein an aerosol can of smoke simulation material. The air impeller, the spray can, and a movable wand are manipulated to direct smoke to the detector's sensor.
While each of these devices is portable, they are too complicated in construction and application to be useful for conducting cursory calibrations of gas detectors. In some circumstances, they may even prove undesirably complicated or expensive for use in full calibration procedures.
Accordingly, it is an object of the present invention to provide an inexpensive, simply operated, easily manageable kit for conducting both cursory and full calibration procedures on gas detectors.